Process automation systems are frequently of modular structure, in other words the overall system is made up of individual modules, specifically components or component assemblies. Various systems can also be extended during operation, so that modules can be added, in particular can be plugged into slots provided for the purpose, without the overall system having to be switched off or stopped. Switching off the system in this manner would be very problematic specifically in the field of process automation and particularly in the field of plant control, since such downtimes naturally result directly in production stoppages.
There are various problems with regard to extending such systems of modular structure during operation. The so-called overload scenario is particularly problematic. Depending on the power consumption of the module to be added, the power supply output for the system may no longer suffice, given the modules already added, to continue to supply all the modules, including the newly added module. If the module is added anyway, this can overload the power supply and result in its collapse. The entire system fails as a result. This overload scenario is frequently detected directly, as soon as the module to be newly added is added.
However in practice there is also a risk that such overload scenarios may only occur some time after the module is added. The cause is then a temperature-dependent overload response by the power supply. If the external temperature is low, the power supply will for example tolerate a higher output power in the long term than at a higher temperature. In this instance the system can switch to an initially tolerated overload range after a module is added at low external temperature, with this only causing the system to be shut down or to collapse, if the external temperature rises. This can happen hours or even days or weeks after module addition in individual instances.
Various measures are known in the prior art to prevent such overload scenarios when extending the systems mentioned in the introduction.
For example for safety reasons a power supply is used, which is of significantly larger dimensions than the actual requirement. This over-dimensioned power supply is intended to prevent the remaining residual power being inadequate for further modules when they have to be added. One disadvantage of this procedure is that this over-dimensioned power supply results in significant additional costs, which could be avoided. And of course power supply systems of greater power take up more space.
Finally it is known that the individual addable modules can be limited in particular on the system side to a maximum power requirement and the number of addable modules can also be limited on the system side. In this instance the power supply is designed for the maximum overall power requirement under such conditions. In other words the power supply is dimensioned so that it supplies adequate power given the maximum power requirement of the individual modules, even if the maximum possible number of modules is added to the system.
This solution also has the disadvantage that the power supply is over-dimensioned for a plurality of instances, for example if not all the module slots of the system are occupied. A significant excess of power is thus made available, resulting in high costs.
In one alternative to this procedure the power supply is not designed for the maximum overall power required but just for an interim power, which is sufficient for most applications. With this solution system failures are again possible, if more modules are added in an exceptional manner in contrast to the application defined as normal, in other words a greater overall power is required than the power supply can supply.